fundamentals of engineering supplied-reference handbook - Ventech!

WASTEWATER TREATMENT AND
TECHNOLOGIES
Activated Sludge
θcY
( So
− Se
)
X A =
, where
θ 1+
k θ
( )
d
c
XA = biomass concentration in aeration tank (MLSS or
MLVSS kg/m 3 );
So = influent BOD or COD concentration (kg/m 3 );
Se = effluent BOD or COD concentration (kg/m 3 );
kd = microbial death ratio; kinetic constant; day −1 ;
typical range 0.1–0.01, typical domestic wastewater
value = 0.05 day –1 ;
Y = yield coefficient Kg biomass/Kg BOD consumed;
range 0.4–1.2; and
θ = hydraulic residence time = Vol / Q
VolX A
θc = Solids residence time =
QwXw + QeXe M ( 100)
Vols = Sludge volume/day:
Qs
=
ρs
( % solids)
Solids loading rate = Q X/A
For activated sludge secondary clarifier Q = Qo + QR
Organic loading rate (volumetric) = QoSo /Vol
Organic loading rate (F:M) = QoSo /(Vol XA)
Organic loading rate (surface area) = QoSo /AM
Sludge volume after
SVI =
MLSS
Type of Process
settling(
mL/L)
( mg/L)
* 1,000
159
ENVIRONMENTAL ENGINEERING (continued)
Steady State Mass Balance around Secondary Clarifier:
(Qo + QR)XA = Qe Xe + QR Xw + Qw Xw
A = surface area of unit,
AM = surface area of media in fixed-film reactor,
Ax = cross-sectional area of channel,
M = sludge production rate (dry weight basis),
Qo = flow rate, influent
Qe = effluent flow rate,
Qw = waste sludge flow rate,
ρs = wet sludge density,
R = recycle ratio = QR/Qo
QR = recycle flow rate = QoR,
Xe = effluent suspended solids concentration,
Xw = waste sludge suspended solids concentration,
Vol = aeration basin volume,
Q = flow rate.
DESIGN AND OPERATIONAL PARAMETERS FOR ACTIVATED-SLUDGE
TREATMENT OF MUNICIPAL WASTEWATER
Mean cell
Volumetric
Food-to-mass ratio
residence
loading
(kg BOD5/kg
time
(Vol-kg
MLSS)
(θc, d)
BOD5/m 3 Hydraulic
Mixed liquor
residence
suspended Recycle
time in
Flow
solids ratio
aeration
regime*
(MLSS, (Qr /Q)
) basin
mg/L)
(θ, h)
BOD5
removal
efficiency
(%)
Air supplied
(m 3 /kg
BOD5)
Tapered aeration 5−15 0.2−0.4 0.3−0.6 4−8 1,500−3,000 0.25−0.5 PF 85−95 45−90
Conventional 4−15 0.2−0.4 0.3−0.6 4−8 1,500−3,000 0.25−0.5 PF 85−95 45−90
Step aeration 4−15 0.2−0.4 0.6−1.0 3−5 2,000−3,500 0.25−0.75 PF 85−95 45−90
Completely mixed 4−15 0.2−0.4 0.8−2.0 3−5 3,000−6,000 0.25−1.0 CM 85−95 45−90
Contact stabilization 4−15 0.2−0.6 1.0−1.2 0.25−1.0 45−90
Contact basin 0.5−1.0 1,000−3,000 PF 80−90
Stabilization basin 4−6 4,000−10,000 PF
High-rate aeration 4−15 0.4−1.5 1.6−16 0.5−2.0 4,000−10,000 1.0−5.0 CM 75−90 25−45
Pure oxygen 8−20 0.2−1.0 1.6−4 1−3 6,000−8,000 0.25−0.5 CM 85−95
Extended aeration 20−30 0.05−0.15 0.16−0.40 18−24 3,000−6,000 0.75−1.50 CM 75−90 90−125
♦ Metcalf and Eddy, Wastewater Engineering: Treatment, Disposal, and Reuse, 3rd ed., McGraw-Hill, 1991 and McGhee, Terence and E.W. Steel, Water Supply and Sewerage, McGraw-Hill, 1991.
*PF = plug flow, CM = completely mixed.